From Archon Arcana - The KeyForge Wiki

When an ability steals Æmber, the stolen Æmber is removed from the opponent’s Æmber pool and added to the Æmber pool of the player resolving the steal ability.

If an ability steals more Æmber than a player has remaining in their pool, the ability steals only the amount remaining in the pool.

KeyForge Master Rulebook v16 November 2022